- Written by: Irfan Sheikh
Must know
EKG artifact
EKG artifacts are charcterized by regular, monophasic, low-amplitude, spiky waveforms that are time-locked with the QRS complexes in the EKG leads.
Myogenic artifact
Myogenic artifacts are characterized by high frequency, ‘spiky’ appearing activity in the anterior (frontal) leads (due to frontalis muscle contraction), or temporal leads (due to temporalis mucle contraction), along with an absence of a physiological field denoting non-cerebral source.
Eye blinks
Eye blinks are characterized by relatively higher amplitude positive/downward deflections that are symmetrically seen in the frontal (anterior) leads maximally (Fp1 and Fp2). The globe of the eye intrinsically has a dipole where the cornea is positive and the retina negative. The conjugate upward movement of the eye globes associated with blinking induces a relatively positive potential at Fp1 and Fp2 electrodes thus generating a positive/downward deflection on EEG, known as Bell's phenomenon.
Eye fluttering
Eye fluttering is chracterized by rhythmic 3-4 Hz activity in the frontal leads (restricted to Fp1 and Fp2 electrodes) that appear similar to eye blinks, albeit in trains.
Lateral eye movements
Lateral eye movements are charcterized by out-of-phase deflections in the anterior leads (Fp1-F7/F7-T3 and Fp2-F8/ F8-T4 electrodes). Due to the intrinsic dipole of the eye globe where the cornea is positive and the retina negative, a right-sided eye movement will cause F8 to be positively charged and F7 to be simultaneously negatively charged, whereas a left-sided eye movement will cause F7 to be positively charged and F8 to be simultaneously negatively charged. The same movements can also be seen as undulating waveforms in the LOC-ROC channel where electrodes are placed on the left outer canthus (LOC) and right outer canthus (ROC).
Electrode pop
An electrode pop is characterized by a high-voltage waveform confined to a single electrode, which can occur due to poor contact of the electrode with skin, poor connection of electrode to the wire, or a fractured lead wire. It tends to be higher amplitude than those of the surrounding electrodes and presents with a rapid rise followed by a slower fall. There is often recurrence within a short time if the affected electrode is not fixed and may have pseudoevolution.
50/60 Hz artifact
50/60 Hz artifact is characterized by diffuse, high-frequency, activity in the 50 or 60 Hz range which is an environmental, electrical artifact produced by AC line frequencies (60 Hz in United States, 50 Hz in Europe). The notch filter can be used to eliminate this artifact.
Lateral rectus spike
A lateral rectus spike is characterized by a vert short, relatively low voltage spiky waveform at the beginning of a fast, lateral eye movement. These are frequently recorded in F7 and F8 electrodes immediately prior to saccadic horizontal or oblique eye movements. This artifactual waveform, which represents an isolated motor unit potential in the lateral rectus muscle, is most noticeable during rapid eye movement (REM) sleep but is also often seen during wakefulness.
Videos
EEG basics:
Normal EEG:
- EEG Talk - Episode 1: Normal Adult EEG
- EEG Talk - Episode 22: Fabio's EEG
- Roadmap to EEGs: Normal EEG
Reference Articles
- Amin U, Nascimento FA, Karakis I, Schomer D, Benbadis SR. Normal variants and artifacts: Importance in EEG interpretation. Epileptic Disord. 2023 Oct;25(5):591-648. PMID 36938895
- Kane N, Acharya J, Benickzy S, et al. A revised glossary of terms most commonly used by clinical electroencephalographers and updated proposal for the report format of the EEG findings. Revision 2017. Clin Neurophysiol Pract. 2017 Aug 4;2:170-185. PMID 30214992
- Ko A, Kong J, Samadov F, et al. Significance of polyspikes on electroencephalography in children with focal epilepsy. Ann Child Neurol. 2022;30(2):45-52. doi:10.26815/acn.2022.00024
- Kural MA, Duez L, Sejer Hansen V, et al. Criteria for defining interictal epileptiform discharges in EEG: A clinical validation study. Neurology. 2020 May 19;94(20):e2139-e2147. PMID 32321764
- Leitinger M, Beniczky S, Rohracher A, et al. Salzburg Consensus Criteria for Non-Convulsive Status Epilepticus--approach to clinical application. Epilepsy Behav. 2015 Aug;49:158-63. PMID 26092326
- Nascimento FA, Beniczky S. Teaching the 6 criteria of the International Federation of Clinical Neurophysiology for defining interictal epileptiform discharges on EEG using a visual graphic. Neurology Education. 2023;2(2):e200073. doi:10.1212/NE9.0000000000200073
- Written by: Doyle Yuan
Must-know
Awake state: Posterior dominant rhythm (PDR)
The posterior dominant rhythm (PDR) is a well-formed, quite symmetric, sinusoidal/rhythmic waveform best observed in the posterior head regions, namely in the occipital channels. The PDR is best seen during wakefulness when eyes are closed/upon eye closure during relaxation or relative mental inactivity, and is attenuated by eye opening.
Please note that the PDR frequency normally progresses as patients age, as shown in the table below. In adults, the normal frequency is in the alpha range.
| Age | Frequency (Hz) |
|---|---|
| 0-1 yrs | 5.3 ± 1.8 |
| 2-3 yrs | 6.8 ± 1.8 |
| 4-5 yrs | 7.9 ± 1.8 |
| 6-7 yrs | 8.7 ± 1.8 |
| 8-15 yrs | 9.5 ± 1.8 |
| 16-50 yrs | 9.9 ± 1.8 |
| >51 yrs | 9.1 ± 1.8 |
Drowsiness: Background/PDR slowing
Transitions in state of consciousness result in changes in frequency, distribution, and amplitude of the dominant background activity. The onset of drowsiness is marked by a decrease in alpha activity and an increase in centrally predominant polymorphic theta activity (5-8 Hz), which should not exceed 30% of the recording in the adult awake state.
Drowsiness: Slow roving eye movements
Horizontal slow roving eye movements may be present during drowsiness. They are seen as out-of-phase waveforms in the anterior leads (Fp1-F7; F7-T3 on the left and Fp2-F8; F8-T4 on the right). The slow roving eye movements can also be seen as undulating waveforms in the LOC-ROC channel where electrodes are placed on the left outer canthus (LOC) and right outer canthus (ROC).
Stage 1/2 sleep: Vertex waves
Vertex sharp waves are surface-negative, spiky/sharp waveforms with maximal negativity at the vertex (Cz). They are normal EEG graphoelements, typically seen during light sleep. They are typically isolated, but trains of repetitive vertex waveforms may occur.
Stage 1/2 sleep: POSTS
Positive occipital sharp transients of sleep (POSTS) have a biphasic morphology (reverse check mark), are surface-positive and occipital, and often appear in brief, semi-rhythmic trains up to 4-5 Hz. They are usually synchronous but asymmetric. POSTS appear during light sleep (stages N1 and N2) and may persist into slow-wave sleep but are virtually never seen during REM sleep.
Stage 2 sleep: Sleep spindles
Sleep spindles appear as bursts of 11 to 16 Hz sinusoidal activity predominantly in the midline and parasagittal regions during light sleep. They first appear around the age of 2 months. These are typically asynchronous until 18-24 months of age after which they become largely synchronous. Sleep spindles are the EEG hallmark of stage N2 sleep although they can also occur during stage N3 sleep. They are hypothesized to be produced by synchronous cortical and thalamic activity during non-REM sleep.
Stage 2 sleep: K complexes
K-complexes are high-amplitude, negative deflections that are frontally predominant and followed by a smaller positive deflection as well as admixed sleep spindles. They are typically seen during stage N2 sleep.
Stage 3 sleep: Diffuse irregular delta slowing
During stage N3 sleep, the majority of each EEG epoch is comprised of continuous, generalized, polymorphic/irregular, high-amplitude (>75 uV), low-frequency (predominantly 1-2Hz delta) waveforms. These are intermixed with spindle activity, and muscle artifact and eye blinks are absent.
Rapid eye movement (REM) sleep: Erratic eye movements
Rapid eye movement (REM) sleep is characterized by a desynchronized EEG pattern with mixed frequencies in the theta to beta range and reduced muscle activity. A characteristic feature of REM sleep is rapid eye movements which are seen in the frontal leads and can be accompanied by a low-voltage spiky waveform called the lateral rectus spike.
Rapid eye movement (REM) sleep: Sawtooth waves
Sawtooth waves, appearing as 2-6 Hz asymmetric, monomorphic waveforms with a serrated appearance, may be present during REM sleep and should not be mistaken for epileptiform activity.
Videos
Set-up and settings:
- Manikin demonstration on how to conduct EEG recordings
- Live demonstration on how to conduct EEG recordings
- EEG Talk - Episode 9: Settings
EEG basics:
Normal EEG:
- EEG Basics - Normal Awake EEG
- EEG Basics - Normal Asleep EEG
- EEG Talk - Episode 1: Normal Adult EEG
- Roadmap to EEGs: Normal EEG
Normal EEG examples:
Reference Articles
- Amin U, Nascimento FA, Karakis I, Schomer D, Benbadis SR. Normal variants and artifacts: Importance in EEG interpretation. Epileptic Disord. 2023 Oct;25(5):591-648. PMID 36938895
- Britton JW, Frey LC, Hopp JL, et al. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society. 2016. PMID 27748095
- Lodder SS, van Putten MJ. Quantification of the adult EEG background pattern. Clin Neurophysiol. 2013 Feb;124(2):228-37. PMID 22917580
- Marcuse LV, Schneider M, Mortati KA, et al. Quantitative analysis of the EEG posterior-dominant rhythm in healthy adolescents. Clin Neurophysiol. 2008 Aug;119(8):1778-1781. PMID 18486545
- Asadi-Pooya AA, Sperling MR. Normal Awake, Drowsy, and Sleep EEG Patterns That Might Be Overinterpreted as Abnormal. J Clin Neurophysiol. 2019 Jul;36(4):250-256. PMID 31274687
- Leitinger M, Beniczky S, Rohracher A, et al. Salzburg Consensus Criteria for Non-Convulsive Status Epilepticus--approach to clinical application. Epilepsy Behav. 2015 Aug;49:158-63. PMID 26092326
- Kane N, AchaLevin KH and Luders HO. Comprehensive clinical neurophysiology, W.B. Saunders Company, Philadelphia, 2000.ya J, Benickzy S, et al. A revised glossary of terms most commonly used by clinical electroencephalographers and updated proposal for the report format of the EEG findings. Revision 2017. Clin Neurophysiol Pract. 2017 Aug 4;2:170-185. PMID 30214992
- Kural MA, Duez L, Sejer Hansen V, et al. Criteria for defining interictal epileptiform discharges in EEG: A clinical validation study. Neurology. 2020 May 19;94(20):e2139-e2147. PMID 32321764
- Nascimento FA, Beniczky S. Teaching the 6 criteria of the International Federation of Clinical Neurophysiology for defining interictal epileptiform discharges on EEG using a visual graphic. Neurology Education. 2023;2(2):e200073. doi:10.1212/NE9.0000000000200073
- Rey V, Aybek S, Maeder-Ingvar M, Rossetti AO. Positive occipital sharp transients of sleep (POSTS): a reappraisal. Clin Neurophysiol. 2009 Mar;120(3):472-5. PMID 19237314
- Nascimento FA, Beniczky S. Sawtooth waves: An EEG normal variant. Epileptic Disord. 2023 Feb;25(1):120-121. PMID 36939686
- Wüstenhagen S, Terney D, Gardella E et al. EEG normal variants: a prospective study using the SCORE system.Clin Neurophysiol Pract. 2022. PMID 35865124
- Krauss GL, Abdallah A, Lesser R, Thompson RE, Niedermeyer E. Clinical and EEG features of patients with EEG wicket rhythms misdiagnosed with epilepsy. Neurology. 2005. PMID 15955937
- Rey V, Aybek S, Maeder-Ingvar M, Rossetti AO. Positive occipital sharp transients of sleep (POSTS): a reappraisal. Clin Neurophysiol. 2009. PMID 19237314
- Written by: Fabio Nascimento
Primary references:
- Schomer DL, Lopes da Silva FH. Niedermeyer's Electroencephalography: basic principles, clinical applications, and related fields. Oxford University Press. 2018.
- Levin KH and Luders HO. Comprehensive clinical neurophysiology, W.B. Saunders Company, Philadelphia, 2000.
- Marcuse LV, Fields MC, Yoo JJ. Rowan’s Primer of EEG 3rd Edition. Elsevier, 2024
- Mecarelli O. Clinical Electroencephalography. Springer, 2019
- Gelisse P, Crespel A. Atlas of electroencephalography. Awake and sleep EEG. Activation procedures and artifacts. John Libbey Eurotext, 2019
Secondary references:
- Husain AM. Current practice of clinical electroencephalography. Wolters Kluwer, 2023
- Louis EKS, Frey LC. Electroencephalography (EEG): an introductory text and atlas of normal and abnormal findings in adults, children, and infants. Chicago: American Epilepsy Society, 2016.
- Stern JM. Atlas of EEG patterns. Wolters Kluwer Lippincott Wiliams & Wilkins, 2013.
- Fisch BJ. Fisch & Spehlmann’s EEG Primer Basic principles of digital and analog EEG. Elsevier, 1999.